Insulating mounting for brush holders and the like



Oct. 19, 1948. E. o. MUELLER ET AL 2,451,969

INSULATING MOUNTING FOR BRUSHHOLDERS AND THE LIKE Filed July 31, 1946 Lf i WITNESSES: E h 0 M INV/E/NTORS a Y r r16 ue er an Dona/a L, 6/6500.

ATTORNEY Patented. Oct. 19 1948 OFFICE INSULATING MOUNTING FOR BRUSH HOLDERS AND 111E LIKE Erich 0. Mueller, Irwin, and Donald L. Gibson,

Pittsburgh, Pal,

assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa, a corporation oi. Pennsylvania Application July 31, 1946, Serial l lo. 687,446

8 Claims. 1

Our invention relates to insulating mountings, and it has particular relation to commutator brushholder mountings for 4000-volt directcurrent locomotive motors, although it is applicable to other uses.

Due to space-limitations in transportationmotors, the size of the brushholder mounting is limited. Creepage surfaces must be held to a minimum. In the design of the 4000-volt motor, a horizontal creepage-distance of three inches between the support and the brushholder is the maximum allowed in the brushholder-mounting. That does not provide a sufficient safety-factor for 4000-vo1t operation. However, it is permissible to increase the actual creepage-distance by utilizing an insulator having a cylindrical outer surface having one or more bulged portions or flanges or skirts, for providing a greater actual creepage-surface length than the axial length of the insulator.

However, it is not practical to properly and satisfactorily provide such a design in a molded insulating connector-member, moldedly interlocking with parts of two metal end-members, and having the bulged or flanged or skirted outer creepage-path, because of the deep draw needed for the mold. Also, in railway practice, glazed porcelain surfaces have been found to be more suitable for a high creepage-insuiation. due to the severe conditions of moisture and dirt in railway motors, as a glazed porcelain surface has better moisture and dirt-resistant creepagecharacteristics than the best creepage-surface characteristic that can readily be given to the molded insulating connector-member. And yet the molded connector-construction has better strength-characteristics than the porcelain.

It is an object of our invention to provide a novel construction and combination which makes it feasible to successfully combine the desirable characteristics of both types of insulation, in a mounting suitable for brushholclers and other electrical devices.

The drawing shows an exemplary embodiment of our invention, in an insulating mounting for a brushholder for a high-voltage direct-current railway-motor, Fig. 1 being a fragmentary endview of the commutator-end of such a-machine, with parts broken away to show the brushholdermounting in section on the line I'-I in Fig. 2,

2 while Fig. 2 is a fragmentary longitudinal section through the machine.

The illustrated motor is a minimum-dimensioned dynamo-electric machine having a voltage sufliciently high to make insulating creepage-distances somewhat diflicult to obtain, particularly with a sufficient factor of safety for the application of the desirable overvoltage tests during the manufacturing operations. It has a field-member 3, within which is rotatably supported an armature member 4, having a commutator 5. Bearing on the commutator are brushes 6, which are carried by brushholders I. The brushholders are supported by our improved insulating brushholder-mountings 8, which are supported from the encl-head 9 of the motor-frame.

Our insulating brushholder-mounting 8 comprises a support-end metal member Ii, adapted to be connected, at it, to the supporting member or frame 9, and an electrical-end metal member i3 which is adapted to be connected, at H, to the brushhoider l or other electrical member to be insulatingiy supported. These two end-members ii and iii of the insulating mounting 8 each have a cylindrical outer surface as shown at H and i3, (defining a cylinder as the surface generated by any straight line moving parallel to a fixed straight line or axis). Between these two metal end-members ii and i3, we provide a molded insulating connector-member i5, moldediy interlocking with parts ii" and I3" of both of said metal end-members, and securely joining the same together in one mechanically joined, but electrically insulated, unit. This insulating connector-member i5 has a cylindrical outer surface I6 which substantially merges with the cylindrical outer surfaces ii and I3 of the metal endmembers II and i3.

In accordance with our invention, we also provide a porcelain creepage-surface insulator i6, fitting over the cylindrical outer surface l5 of the connector-member I5, and having one or more bulged portions i8, of increased outer diameter, for providing a greater actual creepagesurface length, indicated by the curved dotted line I! in Fig. 1, than the axial length 18 of the porcelain; The porcelain insulator l6 has a glazed outer creepage-surface, along which the dotted creepage-line I! has been drawn, and an 3, unglazed bore, which fits over the merging cylindrical surfaces .ll', l", l3.

To successfully utilize the form of construction which has just been described, it is necessary to utilize means for holding the porcelain insulator I! in place, and for so filling the space-between the bore of the porcelain and the cylindrical surfaces ll', l5, II, that any electrical fiashover between the metal end-members II and I! shall always occur over the outer creepage-surface indicated by the curved dotted line H, and never through the space between the bore of the'porce- I lain and the surfaces ll, l8, ii of the metal end-members H and I3 and their molded insulating connector-member ii. To this end, we provide a substantially non-shrinking, insulating adhering-member 20, which substantially completely fills the aforesaid space inside of the bore of the porcelain creepage-surface insulator l8, while being capable of adheringtightly to both the unglazed surface of the bore of the porcelain and the outer cylindrical surface l5 of the molded insulating connector-member l5. This space must be filled with a solid or non-gaseous insulator, because if any gas-filled crack should exist or develop therein, such crack would constitute a shorter fiashover distance or path than the outer creepage-surface indicated by the curved dotted line H. In order for the adhering-member 20 to leave no air-filled fiashover-cracks, it is necessary for it to be substantially non-shrinking on setting. In order to enable it to meet the operating conditions of the motor, it is necessary also for this adhering-member 20 to be resistant to heat, water and oil. It. is desirable also, for this adhering-member 20 to have rubber-like resilient properties, in the finished product, or after setting or curing,.in order to better safeguard,

against the possibility of cracking. v

There are several materials capable of more or less completely fulfilling the above requirements for the adhering-member 20, including an uncured silicon rubber stock, one of the silicon resins with a filler of titanium oxide or other suitable inert pigment. Such products are heatstable, oxidation-resistant, and resilient. They are characterized by their excellent dielectric properties, their moisture-resistance, and their oil-resistance; and they retain their rubberiness at high temperatures (300 F.). They are a dope or cement, having 100% solids, with no solvents; requiring no oxygen or loss of solvent to cure; and retaining (or acquiring) their rubber-like texture on curing, as by baiting, for a suitable number of hours, attemperatures such as 150 0., 200 C. and 225 C., or other suitable temperature. depending upon the precise material used.

We claim as our invention:

1. An insulating mounting comprising a support-end metalmember having a cylindrical outer surface. an electrical-end metal member having a cylindrical outer surface of substantially the same diameter, a molded insulating connectors member moldedly interlocking with parts of both of said metal members and securely joining the same together in one mechanically joined but age-surface length than the axial length of the creepage-surface insulator. and a substantially non-shrinking, heat, water and oil-resistant,insulating adhering-member substantially completely filling the space between the bore of the creepage-surface insulator and the cylindrical outer surface of the connector-member for preventinging a cylindrical outer surface of substantially nector-member having better strength-characelectrically insulated unit, said insulating conhector-member having a cylindrical outer surface substantially merging with the cylindrical outer surfaces of the metal members, a creepagesurface insulator'fitting over the cylindrical outer surface of the connector-member and having.

oneor more bulged portions, of increased outer diameter, for providing a greater actual-creepthe same diameter, a molded insulating connector-member moldedly interlocking with parts of both of said metal members and securely joining the same together in one mechanically Joined but electrically insulated unit, said insulating connector-member having a cylindrical outer surface substantially merging with the cylindrical outer surfaces of the metal members, a creepage-surface insulator fitting over the cylindrical outer surface of the connector-member and having one or more bulged portions, of increased outer diameter, for providing a greater actual creepage-surface length than the axial length of the creepage-surface insulator,. and a substantially non-shrinking, heat, water and oil-resistant, insulating adhering-member substantially completely filling the space between the bore of the creepage-surface insulator and the cylindrical outer surface of the connector-member for preventing electrical fiashover from occurring through said space.

13. The invention as defined-in claim 1, characterized by the material of said insulating conhector-member having better strength -char'acterlstics than the material of said creepage-surface insulator, and the outer creepage-surface of said creepage-surface insulator having better moisture and dirt-resistant creepage-characteristics than the best creepage-surface characteristic that can readily be given to the material of said insulating connector-member.

4. The invention as defined in claim 2, characterized by the material of said insulating conteristics than the material of said creepage-surface insulator, and the outer creepage surface of said creepage-surface insulator having better moisture and dirt-resistant creepage-characteristics than the best creepage-suriace characteristic that can readily be given to the material of said insulating connector-member.

5. The invention as defined in claim 1, characterized by said creepage-surface insulator being porcelain, with a glazed outer creepage-surface and a substantially unglazed bore, and said insulating connector-member being of a molded moldable material having better strength-characteristics, in the finished molded state, than the porcelain. v

6. The invention as defined in claim 2, characterized by said creepage-surface insulator bein: porcelain, with a glazed outer creepage-surface and a substantially unglazed bore, and said insulating connector-member being of a molded moldable material having better strength-characteristics. in the finished molded state, than the porcelain.

BONALD L. GES QN.

The mllawmg refiemmes an @i mwm me me cf this pmaem:

UNITE!) STATES PATENT$ Numbez 1,991,062

Number Name Date Owens Feb. 12, 1935 Blucim Sept. 7, 1943 PATEN'EE Qatmtw Date Benmar: a- Sept. 13, 1937 

